Conventionally, two different methods are known as method for detecting a steering angular velocity. The first method consists in counting the number of pulses generated according to changes in steering angle during a predetermined time period, and determining the steering angular velocity from the results of that counting. The second method consists in counting the cycle of said pulses as well as the high-level or low-level period of the pulses, and determining the steering angular velocity from the time counted.
Known as documentary information of background art relating to conventional art is the Japanese Laid-Open Patent Application No. 2000-85609.
However, the first method has a problem that the detected steering angular velocity is not good accuracy in low speed. And a problem with the second method is that the detected steering angular velocity is not good accuracy in high speed.